Efforts to develop an artificial heart have produced a wide variety of blood pump configurations and/or systems. This particular invention relates to "sac type" pumps in which a deformable sac is utilized to provide the pumping action. Deformation of the sac to reduce its internal volume causes the expelling of the sac contents or a portion thereof through a one way valve. Return of the sac to its original undeformed condition expands its internal volume and causes inflow of fluid into the sac through a one way valve for the next pumping stroke. These types of pumps are analogous to the action of the heart in humans and animals.
Devices of the aforementioned type may be actuated in a variety of ways. Some devices employ pneumatic actuation. Others employ expanding or contracting fluids. Still others employ electrical devices such as solenoids or motors for actuation.
With any type of blood pump system (or device) to be implanted in a human, however, a number of common problems are presented. First of all, the system must be suitable for implantation in that its size and configuration must be such as to be readily accommodated in some body cavity. Inlet and outlet connections to the system should be such as to facilitate connection of the system into the bloodstream to provide the desired pumping action. The inlet and outlet connections must also be relatively simple and reliable. The system must also be highly reliable for long periods of time of continuous use. Finally, flow characteristics of the system should be such as to prevent thrombus formation or clotting in the blood.
Although prior art blood pump devices and/or systems have provided promise in certain respects, most have had sufficiently significant defects as to prevent their successful use. Among these defects has been the presence of a diaphragm-housing junction or discontinuity which frequently results in thrombus formation. Other factors contributing to thrombus formation have been poor internal geometry, poor material choice, and wrinkling during deformation of the sac.
U.S. Pat. No. 4,557,673 (assigned to Novacor Medical Corporation, Oakland, Calif.) discloses a deformable sac blood pump system which substantially reduces or eliminates many of the disadvantages and shortcomings associated with previously developed deformable sac systems. As discussed in detail below, the noted pump system's superior performance is primarily due to (i) the circular pump chamber shape, (ii) the tangential placement of the inflow and outflow ports, and (iii) stable pump sac deformation. These factors result in rapid development of a circular flow or "wash" pattern within the pump chamber during the filling phase (especially at low stroke volumes) which minimizes the likelihood of thrombus formation.
Referring to FIGS. 1-3, the blood pump system of the noted patent comprises a pump 10 having a chamber structure which is generally shown at 12. Structure 12 includes a deformable sac 14 having an annular sidewall 16 and a pair of opposed circular, movable walls 18, 20 (see FIG. 2) joined to the sidewall through flexible convoluted (or curved) wall portions 22, 24, respectively. Fluid is supplied to the sac chamber or annulus 26 through an elongated inlet port 28 and is expelled under pressure through an elongated outlet port 30.
In the noted blood pump 10, the inlet and outlet ports 28, 30 have a substantially circular cross-section throughout their respective lengths and are arranged to direct inlet and outlet flow substantially tangentially with respect to the annular side wall of the sac. The ports 28, 30 are provided with valve means, such as inlet valve 32, to produce the requisite one direction flow valving in the pump. As illustrated in FIG. 2, the inlet valve 32 is disposed in the chamber structure 12 in close proximity to the sac annulus 26 to quickly establish a circular flow pattern that effectively washes the sac annulus 26 and inlet valve 32.
A pair of opposed pusher plates 34, 36 are attached to pump actuator 38 to produce expulsion of fluid from the sac annulus 26. The actuator 38 is mechanically connected to each pusher plate 34, 36 through connecting arms, such as arm 40 connecting the actuator to plate 34.
Completing the description of what is generally shown in FIG. 1, pump 10 has a housing 42 which includes a rigid housing ring 44 and a rigid shell 46 encasing the central region of structure 12. The shell 46 is formed with passages which accommodate the inlet and outlet ports 28, 30 in the sac 14.
An object of the present invention to provide a deformable sac blood pump system which incorporates many of the advantageous features disclosed in the above noted patent, and which provides a number of unique and hitherto unknown features which enhance the system's operational characteristics.
A more specific object of the invention is to provide in such a pump system removable inlet and outlet conduits having valves therein to control the flow into and out of the deformable sac.
A related object of the invention is to provide such a pump system in which the number of interposed biomaterial and step transitions at the interfaces between the valved conduits and pump are minimized.
Another object of the invention is to provide in such a pump system a deformable sac having an inlet port with a tapered section to direct the inlet flow toward the annular wall of the sac during pumping operation, resulting in a uniform flow action which minimizes the likelihood of thrombus formation on inner sac surfaces.
A further object of the invention is to provide such a pump system which rapidly develops a uniform flow pattern within the sac chamber, while maintaining low filling and ejection pressures.
Yet another object of the invention is to provide such a pump system which accommodates a broad range of stroke volumes.